Ganymede’s internal structure after Juno and before JUICE.
- 1Space Sciences Laboratory, University of California, Berkeley, CA, USA
- 2Interdepartmental Center for Industrial Research in Aerospace (CIRI AERO), Alma Mater Studiorum – Università di Bologna, Forlì, Italy
- 3Department of Industrial Engineering, Alma Mater Studiorum – Università di Bologna, Forlì, Italy
- 4Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
- 5Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
- 6Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, Rome, Italy,
- 7Southwest Research Institute, San Antonio, TX, USA
We use the magnetic and gravity field data jointly to place constraints on the internal structure of Ganymede. The magnetic induction constraint comes mostly from the Galileo data, as the Juno flyby occurred when Ganymede was near the center of the magnetodisk, thus leading to low sensitivity to magnetic induction. The gravity field model of Ganymede jointly derived from the Galileo and Juno data to place constraints on Ganymede’s internal structure. Unlike in the previous works, the hydrostaticity was not imposed on the degree-2 gravity coefficients. Thus, despite including additional data from Juno, the uncertainties on the degree-2 coefficients increased. In addition, we explicitly treat the effect of non-hydrostaticity on the derived moment of inertia and find significantly wider confidence intervals on the moment of inertia. This leads to a larger allowed parameter space for the internal structure model.
The new gravity solution confirms the past detection of non-hydrostatic anomalies. In our analysis, localized non-hydrostatic features with amplitudes higher than those found on Titan by the Cassini mission are identified. Titan is a useful comparison case as it shares with Ganymede nearly the same mean radius, mean density, and therefore, surface gravity. Thus, the non-hydrostatic deviations of the same amplitude either in shape or in gravity would correspond to approximately the same level of non-hydrostatic stress. On Titan, the gravity field for degree l > 2 reaches at most 5 mGal (Durante et al., 2019), which is a factor of 5 smaller than the largest anomalies found on Ganymede. One key difference between the two bodies is the lack of atmosphere-based erosion processes on Ganymede. Such erosional processes could have led to faster removal of non-hydrostatic signals at Titan reducing the amplitude of its gravity anomalies. In addition, Titan’s outer shell could be thinner and, therefore, less rigid than that of Ganymede, thus not being able to support as much non-hydrostaticity.
Further insights on Ganymede’s interior will be coming from the JUICE mission in the next decade. Currently, the lack of an accurate shape model prevents separating degree-2 hydrostatic and non-hydrostatic contributions. Combined gravity, topography and rotation data acquired by JUICE will be crucial in determining the non-hydrostatic contribution to the degree-2 field to constrain Ganymede’s internal structure.
How to cite: Ermakov, A., Akiba, R., Gomez Casajus, L., Zannoni, M., Keane, J., Tortora, P., Park, R., Buccino, D., Durante, D., Parisi, M., Stevenson, D., Zhang, Z., Brown, S., Levin, S., and Bolton, S.: Ganymede’s internal structure after Juno and before JUICE., EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10295, https://doi.org/10.5194/egusphere-egu23-10295, 2023.
